Posted by: salamandercandy | February 7, 2007

Feedback: A Note on Sir Karl Popper’s Demarcation of Science

The most informative and useful delineation between those pursuits understood as scientific, such as astronomy, and those of the pseudo-sciences, such as astrology, is that science integrates positive and negative feedback loops. These feedback loops are based on critical analysis, empirical testing, and reformulation of falsifiable statements. This process serves to maximize the accumulation of accurate statements and minimize the accumulation of erroneous statements within an integrated system of statements which describe the physical universe. In other words, the primary function of science, and the thing that makes it different from pseudo-science, is constructive self-criticism. Karl Popper, in his essay “Science: Conjectures and Refutations” (1963), claims that, “…the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability.” (p. 11). While I agree with Popper that testability is a necessary criterion for a theory to be considered scientific, I do not believe that testability represents sufficient criteria. What distinguishes science from other pursuits is how this testability serves the central function of science through positive and negative feedback.

While Popper does recognize the importance of the function of feedback in science, he does not include this in his criteria for separating science from pseudo-science. As pointed out in Thomas Kuhn’s essay, “Logic of Discovery or Psychology of Research?” (1970), Popper’s demarcation criteria do not effectively separate scientific statements from non-scientific ones. Kuhn argues that the pseudo-scientific statements made by practitioners of “crafts” or “arts” such as astrology are often, in fact, falsifiable, refutable, and testable (p. 17) and yet, few would argue that astrology is a valid science. Kuhn then goes on to support his own criteria of demarcation. He asserts that astrology is not a science because it is not based on a “puzzle-solving tradition,” and “…without puzzles, able first to challenge and then to attest to the ingenuity of the individual practitioner, astrology could not have become a science even if the stars had, in fact, controlled human destiny.” (p. 18). While Kuhn’s ultimate conclusions are questionable, his criticism is valid. How can falsifiabilty be the criterion separating scientific statements from pseudo-scientific statements, when statements made by astrologers are clearly often falsifiable, and often, in fact, falsified?

I propose, and I think “Sir Karl” would agree, that what makes astrology fundamentally different from science is that the results of falsifiable tests of the statements based on the astrological system do not feedback to inform reevaluation and reformation of the original statements or of the system on which they were based. In other words, Karl Popper’s demarcation criteria, that “…statements or systems of statements, in order to be ranked as scientific, must be capable of conflicting with possible or conceivable, observations,” (p. 12) is a necessary condition of science, but is not, in and of itself, a sufficient demarcation between science and pseudo-science. It becomes sufficient, however, when you add the requirement of feedback… If such statements are tested and found to conflict with verifiable, observable and repeatable empirical evidence, the statements or the premises upon which the statements were made must be reexamined and reformulated.

In presenting his criterion of falsifiabilty, Popper implies, and I agree, that falsification of statements based on negative evidence is the only unequivocal means of creating feedback for the reformulation of scientific statements. What Popper fails to address satisfactorily, is how, in the absence of such negative, unequivocal evidence, a scientific statement becomes accepted. While he mentions briefly that, “Confirming evidence should not count except when it is the result of a genuine test of the theory…” (his emphasis, p. 11), I believe that he glosses over the concept of confirming evidence as having a place in the scientific process, and more importantly, having a role in the determination of what is, and what is not scientific knowledge. He does not address how this form of “corroborating evidence” informs the body of scientific knowledge and contributes to the formation of new scientific statements for future testing. This is an important issue because it is often the totality of such statements that represents the current state of scientific knowledge, and serves the utilitarian and applied functions of science. Thus the feedback aspect of the scientific process must include both negative feedback, in the form of falsification of statements, as well as positive feedback, in the form of corroborative evidence. The dynamic nature of scientific growth and change is dependent on the integration and interaction of these two feedback loops, and to ignore them, or leave them out of the definition of what science is, and what it is not, is to present an incomplete picture.

Just as the frequency of deleterious genetic mutations may be reduced in a gene pool by the processes of natural selection, the frequency of erroneous statements is reduced within the dynamic hierarchical network of scientific knowledge by the processes of critical analysis, testing, and error ramification. It is important to recognize that erroneous statements in science, just like deleterious genes in populations, will always exist, and some may be impossible to eliminate entirely. However, the process of science, unlike the activities of the pseudo-sciences, serves to provide sufficient selective pressure, in the form of critical analysis, empirical testing, and the positive and negative feedback of results of such testing and analysis, to minimize erroneous statements, and to maximize accurate statements. In this way, science, above all other approaches, represents an effective means to increase the accuracy of our knowledge of the physical universe.



  1. that was impressive clarity! thank you for the post….

    – Dr.Namyata Pathak

  2. could you give me an outline regarding the logic of scientific discovery by karl popper

  3. A very nice prolongation on Popper, which I find very interesting. (Although I don’t hold the problem of demarcation for a very interesting one.) Let me however disagree with you.

    One should point out that this feedback aspect of refutation was, I think, always in the background of Popper’s criterion. In numerous works (in fact all of them), he has stressed the importance of the critical attitude. The critical attitude can be interpreted as allowing the dismissal of refuted theories, i.e. allowing what you call “negative feedback” on theories.

    As you mentioned, this criterion is not expressly included in the criterion of scientificity. But one could then argue that it might have been left out intentionally. I can see two reasons why it might have been the case.

    First, feedbacks are about disciplines and people. Saying that *astrology* does not subject itself to feedbacks merely means that *astrologists* does not take refutations into account to improve the way they make statements.
    However, Karl Popper’s goal was to find a criterion *about statements*, rather than disciplines (he has critized the existence and fruitfulness of separating things into disciplines). In other words, the goal of the criterion was to sort statements/theories. It is a criterion that applies to the objects of World 3, the world of theories.

    Secondly, the notion of feedback does not provide a clear-cut criterion, by which one can end up with a binary classification (science vs. non-science). As it is more a criterion about people and disciplines, it is blurry. People being open to criticism is a matter of degree I believe, some people are very open, some people are not, some people only a little. And it would then be hard to find an indisputable limit of “openness to criticism” to sort what is science from what is not.
    (And once again, we would be talking here about disciplines and people, rather than specific statements.)

    Because of these two reasons, I don’t think the possibility of feedbacks can provide a further criterion of scientificity.

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